HEALTH INFORMATION

Flavonoids

Uses

Flavonoids are a class of water-soluble plant pigments. Flavonoids are broken
down into categories, though the issue of how to divide them is not universally
agreed upon. One system breaks flavonoids into isoflavones, anthocyanidins,
flavans, flavonols, flavones, and flavanones.1 Some of the best-known flavonoids, such as genistein in soy,
and quercetin in onions, can be considered subcategories of categories. Although
they are all structurally related, their functions are different. Flavonoids
also include hesperidin, rutin, citrus flavonoids, and a variety of other
supplements.

Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

1 StarFor an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

This supplement has been used in connection with the following health conditions:

Used for

Why

3 Stars

Chronic Venous Insufficiency

500 mg hydroxyethylrutosides twice per day

Flavonoids strengthen capillaries. A flavonoid derived from rutin, called HR, has been shown to be effective in clearing leg swelling and reducing other CVI symptoms.

Flavonoids promote venous strength and integrity. Most trials of flavonoids in patients with CVI have used a type of flavonoid called hydroxyethylrutosides (HR), which is derived from rutin. These double-blind and other controlled trials have consistently shown a beneficial effect of HR in clearing leg swelling and other signs of CVI.2, 3, 4 Positive results from a double-blind trial have been obtained using 500 mg of HR taken twice per day for 12 weeks.5 In this trial, the preparation was found to add further benefit to that provided by compression stockings commonly used to treat CVI. Similar results were obtained in another controlled trial.6 It is unclear whether other flavonoids are as effective as HR for CVI. HR has also been used successfully as a topical preparation for the treatment of CVI.7

3 Stars

Hepatitis

500 to 750 mg daily of catechins

The flavonoid catechin has helped people with acute viral hepatitis, as well as people with chronic hepatitis.

Catechin, a flavonoid, has helped people with acute viral hepatitis,8 as well as individuals with chronic hepatitis,9 though not all trials have found a benefit.10 A typical amount used in successful trials is 500–750 mg three times per day. Although catechin is found in several plants, none contain sufficient amounts to reach the level used in the trials; thus, catechin supplements are needed. However, because of its potential to cause side effects on rare occasions,11 catechin should be used only under medical supervision.

2 Stars

Bruising

400 to 800 mg hesperidin with vitamin C daily

Flavonoids are often recommended with vitamin C. Flavonoids are vitamin-like substances that can help strengthen capillaries and therefore may also help with bruising.

Doctors often suggest that people who experience easy bruising supplement with 100 mg to 3 grams of vitamin C per day for several months. Controlled research is limited, but vitamin C supplements have been shown to reduce bruising in people with low vitamin C intake.12Flavonoids are often recommended along with vitamin C. Flavonoids are vitamin-like substances that can help strengthen capillaries and therefore may also help with bruising.13 Flavonoids may also increase the effectiveness of vitamin C; citrus flavonoids, in particular, improve the absorption of vitamin C. Older preliminary research suggested that vitamin C, 400–800 mg per day, in combination with 400–800 mg per day of the flavonoid, hesperidin, reduced bruising in menopausal women.14 A small, preliminary trial in Germany gave three people with progressive pigmented purpura (a chronic bruising disorder) 1,000 mg per day of vitamin C and 100 mg per day of the flavonoid rutoside. After four weeks, noticeable bruising was no longer apparent and did not recur in the three month period after treatment was stopped.15 Controlled research is needed to better establish whether vitamin C and flavonoids are effective for easy bruising.

2 Stars

Cold Sores (Vitamin C)

200 mg with 200 mg flavonoids, three to five times daily

Vitamin C plus flavonoids may help speed cold sore healing.

Vitamin C has been shown to inactivate herpes viruses in the test tube.16 In one study, people with herpes infections received either a placebo or 200 mg of vitamin C plus 200 mg of flavonoids, each taken three to five times per day. Compared with the placebo, vitamin C and flavonoids reduced the duration of symptoms by 57%.17

Supplementing with a combination of vitamin B3, vitamin C, and the flavonoid rutin resulted in a 90% effectiveness for relieving menstrual cramps in one study.

The niacin form of vitamin B3 has been reported to be effective in relieving menstrual cramps in 87% of a group of women taking 200 mg of niacin per day throughout the menstrual cycle.18 They then took 100 mg every two or three hours while experiencing menstrual cramps.19 In a follow-up study, this protocol was combined with 300 mg of vitamin C and 60 mg of the flavonoid rutin per day, which resulted in a 90% effectiveness for relieving menstrual cramps. Since these two preliminary studies were published many years ago, no further research has explored the relationship between niacin and dysmenorrhea. Niacin may not be effective unless taken for seven to ten days before the onset of menstrual flow.

2 Stars

Gingivitis (Vitamin C)

300 mg of vitamin C, plus 300 mg of flavonoids daily

In one study, supplementing with vitamin C plus flavonoids improved gum health in a group of people with gingivitis.

People who are deficient in vitamin C may be at increased risk for periodontal disease.20 When a group of people with periodontitis who normally consumed only 20–35 mg of vitamin C per day were given an additional 70 mg per day, objective improvement of periodontal tissue occurred in only six weeks.21 It makes sense for people who have a low vitamin C intake (e.g., people who eat few fruits and vegetables) to supplement with vitamin C in order to improve gingival health.

For people who consume adequate amounts of vitamin C in their diet, several studies have found that supplemental vitamin C has no additional therapeutic effect. Research,22 including double-blind evidence,23 shows that vitamin C fails to significantly reduce gingival inflammation in people who are not vitamin C deficient. In one study, administration of vitamin C plus flavonoids (300 mg per day of each) did improve gingival health in a group of people with gingivitis;24 there was less improvement, however, when vitamin C was given without flavonoids. Preliminary evidence has suggested that flavonoids by themselves may reduce inflammation of the gums.25

2 Stars

Hemorrhoids

600 to 4,000 mg hydroxyethylrutosides daily or 1 to 3 grams of a mixture of 90% diosmin and 10% hesperidin

Supplementing with flavonoids may reduce symptoms. A number of flavonoids have been shown to have anti-inflammatory effects and to strengthen blood vessels

A number of flavonoids have been shown to have anti-inflammatory effects and/or to strengthen blood vessels. These effects could, in theory, be beneficial for people with hemorrhoids. Most,26, 27, 28, 29 but not all,30 double-blind trials using a group of semisynthetic flavonoids (hydroxyethylrutosides derived from rutin) have demonstrated significant improvements in itching, bleeding, and other symptoms associated with hemorrhoids when people used supplements of 600–4,000 mg per day.

Other trials have evaluated Daflon, a product containing the food-derived flavonoids diosmin (90%) and hesperidin (10%). An uncontrolled trial reported that Daflon produced symptom relief in two-thirds of pregnant women with hemorrhoids.31 Double-blind trials have produced conflicting results about the effects of Daflon in people with hemorrhoids.32, 33 Amounts of flavonoids used in Daflon trials ranged from 1,000 to 3,000 mg per day. Diosmin and hesperidin are available separately as dietary supplements.

Some doctors recommend flavonoid supplements for people with hemorrhoids. However, many different flavonoids occur in food and supplements, and additional research is needed to determine which flavonoids are most effective against hemorrhoids.

2 Stars

Hypertension

300 mg per day of hesperidin, for 4 weeks

A study has found that hesperidin, a flavonoid found primarily in oranges and other citrus fruits, decreased diastolic blood pressure in healthy, overweight males.

Hesperidin is a flavonoid found primarily in oranges and other citrus fruits. In a placebo-controlled trial, supplementation with approximately 300 mg per day of hesperidin for 4 weeks significantly decreased diastolic blood pressure by an average of 3.2 mm Hg in healthy, overweight males. Hesperidin had no effect on systolic blood pressure.34

2 Stars

Ménière’s Disease

Refer to label instructions

Certain flavonoids, known as hydroxyethylrutosides, have been reported to improve symptoms of Ménière’s disease, including hearing problems.

Certain flavonoids, known as hydroxyethylrutosides (HR), have been reported to improve symptoms of MD in one double-blind study. In this study, 2 grams per day of HR for three months resulted in either stabilization of or improvement in hearing.35 Other types of flavonoids have not been studied as treatments for MD.

Some cases of MD are associated with otosclerosis,36, 37, 38, 39 a disease affecting the small bones of the inner ear. Otosclerosis often goes undiagnosed in people with MD, although the coexistence is well documented.40 While preliminary reports suggest otosclerosis may be a cause of MD,41, 42 the relationship between these two conditions remains unclear. Sodium fluoride, a mineral compound available only by prescription, is reported to improve otosclerosis.43, 44, 45, 46 In a preliminary study,47 people with MD and otosclerosis were given supplements of 50 mg of sodium fluoride, 200 mg calcium carbonate, and a multiple vitamin supplying 400–800 IU of vitamin D per day, for periods ranging from six months to over five years. Many participants also had blood sugar abnormalities, and were asked to follow a modified hypoglycemia diet as described above. Significant improvement in vertigo was reported within six months, but improvements in hearing required one to two years. Because most participants used both diet and supplements, the importance of fluoride, calcium, and/or vitamin D to the overall results of this trial is unclear.

2 Stars

Skin Ulcers (Hesperidin, Diosmin)

900 mg per day of diosmin and 100 mg per day of hesperidin

One trial found that a combination of the flavonoids diosmin and hesperidin promoted healing of venous leg ulcers. Hydroxyethylrutosides (related flavonoids) may also help.

A double-blind trial found that a combination of 900 mg per day of diosmin and 100 mg per day of hesperidin, two members of the flavonoid family, resulted in significantly greater healing of venous leg ulcers after two months.53, 54 Related flavonoids known as hydroxyethylrutosides have also been investigated for venous ulcer healing. While one controlled study reported significant additional benefit when 2,000 mg per day of hydroxyethylrutosides were added to compression stocking therapy,55 another double-blind trial using 1,000 mg per day found no effect on ulcer healing;56 a second double-blind trial found no effect of 1,000 mg per day hydroxyethylrutosides on the prevention of venous ulcer recurrences.57

1 Star

Allergies and Sensitivities

Refer to label instructions

Test tube and animal studies have found some effects from natural antihistamines such as flavonoids, though no clinical research has shown whether these substances can specifically reduce allergic reactions.

Many of the effects of allergic reactions are caused by the release of histamine, which is the reason antihistamine medication is often used by allergy sufferers. Some natural substances, such as vitamin C58, 59 and flavonoids,60 including quercetin,61, 62 have demonstrated antihistamine effects in test tube, animal, and other preliminary studies. However, no research has investigated whether these substances can specifically reduce allergic reactions in humans.

1 Star

Capillary Fragility

Refer to label instructions

Flavonoids may help strengthen weakened capillaries, possibly by protecting collagen, one of the most important components of capillary walls.

Compounds called flavonoids may help strengthen weakened capillaries. In test tube and animal studies, they have been shown to protect collagen, one of the most important components of capillary walls.63, 64 A preliminary study found that proanthocyanidins (flavonoids extracted from grape seeds), 150 mg per day, increased capillary strength in people with hypertension and/or diabetes.65 A double-blind trial found a combination of two flavonoids (900 mg per day of diosmin and 100 mg per day hesperidin) for six weeks reduced symptoms of capillary fragility.66 Use of vitamin C with flavonoids, particularly quercetin, rutin, and hesperidin, is sometimes recommended for capillary fragility.67 Doctors often recommend 400 mg of rutin or quercetin three times per day or 1 gram of citrus flavonoids three times per day.

1 Star

Gingivitis

Refer to label instructions

Shown to be effective against gingivitis when taken with vitamin C, flavonoids also appear to be effective by themselves at reducing gum inflammation.

People who are deficient in vitamin C may be at increased risk for periodontal disease.68 When a group of people with periodontitis who normally consumed only 20–35 mg of vitamin C per day were given an additional 70 mg per day, objective improvement of periodontal tissue occurred in only six weeks.69 It makes sense for people who have a low vitamin C intake (e.g., people who eat few fruits and vegetables) to supplement with vitamin C in order to improve gingival health.

For people who consume adequate amounts of vitamin C in their diet, several studies have found that supplemental vitamin C has no additional therapeutic effect. Research,70 including double-blind evidence,71 shows that vitamin C fails to significantly reduce gingival inflammation in people who are not vitamin C deficient. In one study, administration of vitamin C plus flavonoids (300 mg per day of each) did improve gingival health in a group of people with gingivitis;72 there was less improvement, however, when vitamin C was given without flavonoids. Preliminary evidence has suggested that flavonoids by themselves may reduce inflammation of the gums.73

1 Star

Glaucoma

Refer to label instructions

The flavonoid rutin may increase the effectiveness of conventional medication in people with glaucoma.

Many years ago, the flavonoid rutin was reported to increase the effectiveness of conventional medication in people with glaucoma.74 The amount used—20 mg three times per day—was quite moderate. In that study, 17 of 26 eyes with glaucoma showed clear improvement. Modern research on the effects of rutin or other flavonoids in people with glaucoma is lacking.

1 Star

Measles

Refer to label instructions

Flavonoids are nutrients found in the white, pithy parts of fruits and vegetables. Certain flavonoids have been found to inhibit the infectivity of measles virus in the test tube.

Flavonoids are nutrients found in the white, pithy parts of fruits and vegetables. In preliminary laboratory research, certain flavonoids have been found to inhibit the infectivity of measles virus in the test tube.75 Whether flavonoid supplements could be effective in preventing or treating measles is unknown.

1 Star

Menopause

Refer to label instructions

A preliminary trial reported that a combination of vitamin C and the flavonoid hesperidin helped relieve hot flashes in menopausal women.

In 1964, a preliminary trial reported that 1,200 mg each of vitamin C and the flavonoid hesperidin taken over the course of the day helped relieve hot flashes.76 Although placebo effects are strong in women with hot flashes, other treatments used in that trial failed to act as effectively as the flavonoid/vitamin C combination. Since then, researchers have not explored the effects of flavonoids or vitamin C in women with menopausal symptoms.

1 Star

Menorrhagia

Refer to label instructions

Flavonoids protect capillaries (small blood vessels) from damage. In so doing, they might protect against the blood loss of menorrhagia.

Both vitamin C and flavonoids protect capillaries (small blood vessels) from damage. In so doing, they might protect against the blood loss of menorrhagia. In one small study, 88% of women with menorrhagia improved when given 200 mg vitamin C and 200 mg flavonoids three times per day.77 In another study, 70% of women with excessive menstrual bleeding experienced at least a 50% reduction in bleeding after taking a flavonoid product.78 The preparation used in this study contained 90% diosmin and 10% hesperidin and was given in the amount of 1,000 mg per day, beginning five days prior to the expected start of menstruation and continuing until the end of bleeding for three cycles.

1 Star

Retinopathy

Refer to label instructions

Quercetin has been shown to inhibit aldose reductase, an enzyme that appears to contribute worsen diabetic retinopathy. Another flavonoid, rutin, may also improve retinopathy.

Quercetin (a flavonoid) has been shown to inhibit the enzyme, aldose reductase.79 This enzyme appears to contribute to worsening of diabetic retinopathy. However, because the absorption of quercetin is limited, it is questionable whether supplementing with quercetin can produce the tissue levels that are needed to inhibit aldose reductase. Although human studies have not been done using quercetin to treat retinopathy, some doctors prescribe 400 mg of quercetin three times per day. Another flavonoid, rutin, has been used with success to treat retinopathy in preliminary research.80

1 Star

Varicose Veins

Refer to label instructions

Taking hydroxyethylrutoside may help reduce the size of varicose veins associated with pregnancy.

A controlled clinical trial found that oral supplementation with hydroxyethylrutosides (HR), a type of flavonoid that is derived from rutin, improved varicose veins in a group of pregnant women.81 Further research is needed to confirm the benefits observed in this preliminary trial. A typical amount of HR is 1000 mg per day.

How It Works

How to Use It

Flavonoid supplements are not required to prevent deficiencies in people eating a healthy diet. Healthcare practitioners commonly recommend 1,000 mg of citrus flavonoids taken one to three times per day. Alternatively, 240–600 mg of bilberry (standardized to 25% anthcyanosides) may be taken per day.

Where to Find It

Flavonoids are found in a wide range of foods. For example, flavanones are in citrus, isoflavones in soy products, anthocyanidins in wine and bilberry, and flavans in apples and tea.

Possible Deficiencies

Flavonoid deficiencies have not been reported.

Interactions

Interactions with Supplements, Foods, & Other Compounds

The flavonoids work in conjunction with vitamin C. Citrus flavonoids, in particular, improve the absorption of vitamin C.82, 83

Interactions with Medicines

Replenish Depleted Nutrients

Reduce Side Effects

Support Medicine

The flavonoids quercetin, quercitrin, and apigenin enhanced the antiviral activity of acyclovir in test tube studies.84 Controlled research is needed to determine whether taking quercetin or other flavonoid supplements would increase the effectiveness of acyclovir in humans.

Reduces Effectiveness

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.86 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Potential Negative Interaction

Preliminary research in animals found that the citrus flavonoid tangeretin, found primarily in the peel of citrus fruits, interferes with the ability of tamoxifen to inhibit tumor growth.85 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.87 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.88 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.89 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.90 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.91 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.92 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Testolactone

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.93 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.94 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.95 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Explanation Required

none

The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Side Effects

No consistent side effects have been linked to the flavonoids except for catechin, which can occasionally cause fever, anemia from breakdown of red blood cells, and hives.96, 97 These side effects subsided when treatment was discontinued.

In 1980, quercetin was reported to induce cancer in animals.98 Most further research did not find this to be true, however.99, 100 While quercetin is mutagenic in test tube studies, it does not appear to be mutagenic in animal studies.101 In fact, quercetin has been found to inhibit both tumor promoters102 and human cancer cells.103 People who eat high levels of flavonoids have been found to have an overall lower risk of getting a wide variety of cancers,104 though preliminary human research studying only foods high in quercetin has found no relation to cancer risk one way or the other.105 Despite the confusion, in recent years experts have shifted their view of quercetin from concerns that it might cause cancer in test tube studies to guarded hope that quercetin has anticancer effects in humans.106

74. Stocker FW. Clinical experiments with new ways of influencing the intraocular tension. II. Use of rutin to enhance the tension-reducing effect of miotics by reducing the permeability of the blood-aqueous barrier. Arch Ophthalmol 1949;73:429-35.

The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2015.

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